Authentication in the Elastic Stack security features is handled by one or more
authentication services called realms. A realm is used to resolve and
authenticate users based on authentication tokens. The security features
provide the following built-in realms:

native

An internal realm where users are stored in a dedicated Elasticsearch index.
This realm supports an authentication token in the form of username and password,
and is available by default when no realms are explicitly configured. The users
are managed via the user management APIs.
See Native user authentication.

ldap

A realm that uses an external LDAP server to authenticate the
users. This realm supports an authentication token in the form of username and
password, and requires explicit configuration in order to be used. See
LDAP user authentication.

active_directory

A realm that uses an external Active Directory Server to authenticate the
users. With this realm, users are authenticated by usernames and passwords.
See Active Directory user authentication.

pki

A realm that authenticates users using Public Key Infrastructure (PKI). This
realm works in conjunction with SSL/TLS and identifies the users through the
Distinguished Name (DN) of the client’s X.509 certificates. See PKI user authentication.

file

An internal realm where users are defined in files stored on each node in the
Elasticsearch cluster. This realm supports an authentication token in the form
of username and password and is always available. See File-based user authentication.

saml

A realm that facilitates authentication using the SAML 2.0 Web SSO protocol.
This realm is designed to support authentication through Kibana and is not
intended for use in the REST API. See SAML authentication.

kerberos

A realm that authenticates a user using Kerberos authentication. Users are
authenticated on the basis of Kerberos tickets. See Kerberos authentication.

The Elastic Stack security features also support custom realms. If you need to
integrate with another authentication system, you can build a custom realm
plugin. For more information, see
Integrating with other authentication systems.

Realms that are internal to Elasticsearch and don’t require any
communication with external parties. They are fully managed by Elastic Stack
security features. There can only be a maximum of one configured realm per
internal realm type. The security features provide two internal realm types:
native and file.

External

Realms that require interaction with parties/components external to
Elasticsearch, typically, with enterprise grade identity management systems. Unlike
internal realms, there can be as many external realms as one would like - each
with its own unique name and configuration. The Elastic Stack security features
provide the following external realm types: ldap, active_directory, saml,
kerberos, and pki.